Despite the advancements in technologies, wireless communication technologies using the millimeter wave (also referred to as mmWave) are still facing certain technical difficulties. Basically, the first problem that use of the millimeter wave may encounter is severe attenuation of wave energy during transmission, which is highly related to millimeter wave communication systems operated in high frequency bands while using a sizable bandwidth for communication. More specifically, the millimeter wave communication systems use the frequency band with relatively high frequency for communication as compared to the third generation (3G) or the fourth generation (4G) communication systems which are commonly used nowadays. It can be known that an energy intensity of an electromagnetic wave signal received by a receiver is inversely proportional to a square of a signal transmitting distance and is proportional to a wavelength of the electromagnetic wave signal, such that the attenuation degree of the signal energy will be significantly increased if the millimeter wave communication systems use the high frequency signal with short wavelength. Also, the high frequency signal will also cause sudden reduction in the antenna aperture, which may result in decrement of the signal energy of the transmitting signal in the millimeter wave communication systems. Therefore, in order to ensure the communication quality, a transceiver in the millimeter wave systems usually requires use of a multiple antenna beamforming technology to reduce the attenuation of the signal energy, so as to improve the efficiency for gaining the transceiving signals.
Multiple antenna beamforming technology is an antenna device (for example, Active Phased Array Antenna) including multiple antenna units disposed on a base station/user facility, and the antenna units are controlled to make the base station/use facility to produce a beam with directivity. The beamforming technologies accomplished by the antenna array is one of the key factors for influencing performance of a millimeter wave wireless communication system. In order to accurately adjust the shape and direction of the beam, before the amplitude and phase of the corresponding antenna unit are adjusted, the electrical difference used to feed the RF signal to the path of antenna unit needs to be calibrated. Typically, a near-field probe may be used to measure the radiated power density of each of the antenna units to calibrate the antenna unit, or to exhaustively measure the voltage of each of the antenna units at each different phase to create a lookup table, and each of the antenna units is calibrated according to the lookup table. However, conventional calibration methods are found to have a number of problems, for example, the calibration method using near-field probes can only be performed at limited sites (e.g., a qualified electronic device calibration laboratory). On the other hand, when the total number of antenna units is too large, the calibration method using the lookup table will consume a large amount of computing operations.